Oxidation reactions typically involve reacting a hydrocarbon with oxygen in the presence of a catalyst to form an oxygenate. Examples include the conversion of methane to methanol or formaldehyde; ethane or ethylene to ethyl alcohol, ethylene oxide, acetic acid or vinyl acetate; or propylene to acrylic acid or acrolein. Ammoxidation reactions typically involve reacting a hydrocarbon with oxygen and ammonia in the presence of a catalyst to form a nitrile. Examples include the conversion of propane or propylene to acrylonitrile, and isobutane or isobutylene to methacrylonitrile.
A problem with each of these reactions is that they are exothermic and are typically conducted in fixed bed reactors where hot spots tend to form. The formation of these hot spots lowers selectivity towards the desired main product in favor of parallel reactions that form undesired products such as carbon oxides (i.e., CO, CO2). The present invention provides a solution to this problem by conducting the reaction in a microchannel reactor wherein the tendency to form hot spots is reduced and selectivity to the desired product is enhanced. Enhanced selectivity with the inventive process is believed to be due at least in part to the fact that the microchannel reactor provides enhanced heat transfer characteristics and more precise control of residence times. Also, the internal dimensions of the microchannel reactor can be set at a level equal to or below the quench diameter for unwanted reactions.
With the inventive process it is possible to obtain relatively high heat and mass transfer rates and shorter contact times as compared to prior art processes wherein microchannel reactors are not used. This provides for more precise temperature control as compared to such prior art. This, in turn, leads to reduced peak temperatures and a reduction in the formation of undesired by-products. With this process, it is possible to obtain relatively high levels of conversion of the hydrocarbon reactant and high levels of selectivity to the desired product as compared to such prior art.